This invention relates to mixtures of water-soluble, fiber-reactive, yellow, azo dyestuffs with superior color yield and improved build-up properties. Color yield as used in this specification is the amount of color spectrally measured in standard color density units imparted by the dyestuff to a fabric or other substrate. Build-up is the ability of a dyestuff to continue to yield deeper or darker shades of a color as the concentration of the dyestuff in the dye bath is increased which is also expressed in color density units.
Typically, the color yield of an admixture of azo-dyestuffs is proportional to the solar yield and the amount of the components in the mixture. In general the color yield of a mixture will not exceed the color yield of the strongest component of the mixture. Surprisingly, we have found that the color yield of the azo dyestuff mixtures of this invention are significantly higher than the color yield of individual components. Secondly, these mixtures of the invention have improved build-up properties over the individual components.
An exception to this general rule is reported in British Pat. No. 2,108,141 wherein certain mixtures of blue, monoazo disperse dyes are reported having good build-up properties and high tinctorial strength superior to the effect achieved by the application of any single component of the dye mixture. U.S. Pat. No. 4,548,613 reports that certain mixtures of monoazo, yellow disperse dyes (CI Disperse Yellow 54 and 64) produce dyeings of high tinctorial strength, and high dye bath exhaustion. U.S. Pat. No. 4,427,413 discloses other mixtures of these same disperse dyes (CI Disperse Yellow 54 and 64) with improved build-up and better yields in transfer printing. Although these exceptions to the general rule report improved higher color yield or other improved properties they are exceptions.